The invention relates to an inflatable seat belt for securing an occupant in a motor vehicle. The seat belt includes a belt strap, which is divided by way of a belt latch into a diagonal region resting against an occupant""s upper body and into a horizontal region resting against the occupant""s pelvis. These two ends are connected with the vehicle. The belt strap is connected with the belt latch by a fastener having a defined holding force. A belt buckle is fastened to the vehicle into which the belt latch can be detachably connected. A first retractor is fastened to the vehicle into which the diagonal region of the belt strap is connected. A second retractor is fastened to the vehicle into which the horizontal region of the belt strap is connected. An air bag is fastened to the diagonal region of the belt strap and extends from the occupant""s upper body to behind the head. The air bag comprises a material which, during the inflating, is shortened in the axial direction.
An inflatable seat belt is disclosed in International Patent Publication WO 98 00314 A. In this known seat belt, the belt strap is connected with the belt latch by a tear seam, a snap fastener or a button. In the event of an accident and the inflation of the air bag, the connection between the belt strap and the belt latch is opened, so that the horizontal region of the belt strap can be pulled tight. As a result, freedom of movement of the concerned occupant is further limited, and the occupant is prevented from slipping through under the horizontal region of the belt strap. During full brake application, similar high deceleration forces can also occur. The connection between the belt strap and the belt latch can also be opened up. Since this connection is constructed as a destructible fastener, the release or separation process is not reversible. When the belt strap is no longer fixed with respect to the belt latch, the position of the air bag fastened thereon is no longer defined with respect to the occupant. When the seat belt is secured, it is possible that one of the two retractors may wind up too little of the belt strap while the other may wind up too much, with the result that the air bag is arranged too high or too low with respect to the occupant.
In the secured condition of the seat belt, the air bag is arranged too high such that it extends around the deflection fitting, it may be destroyed during the inflating. As a result, the air bag would be ineffective during an impact.
It is an object of the invention to further develop the air bag of the above-mentioned type such that, while the displaceability of the belt strap with respect to the belt latch is maintained, it is ensured that when a defined load is exceeded, in the secured condition of the seat belt, the air bag is always at a defined height.
According to the invention, this object is achieved by providing that the belt strap is connected with the belt latch by a clamping fastener, and the clamping fastener and the first retractor are electrically controllable such that (i) the first retractor as well as the clamping fastener are releasable, (ii) after the withdrawal of a defined length of the belt strap, the first retractor is locked, (iii) after the insertion of the belt latch into the belt buckle, the clamping fastener is locked and the first retractor is released, and (iv) in the event of an impact of the vehicle, the clamping fastener is released.
As a result of these measures, it is ensured that the air bag, or the inflatable region of the seat belt, will always be in the upper position in which the occupant""s head is optimally protected. In addition, it is ensured that, for maintaining a maximal head protection, the diagonal region of the belt strap can only be withdrawn from the upper retractor when, after locking the seat belt and the clamping fastener, the occupant moves his upper body toward the front. As soon as the occupant has returned into his rest position, the upper retractor will pull the slack from the diagonal region of the belt strap. The comfort of a conventional three-point system will therefore also be retained.
In a particularly advantageous embodiment of the invention, it is provided that the belt latch is non-displaceably held in the longitudinal direction of the belt strap and the holding system is designed such that it becomes ineffective when a certain axial force in the diagonal region is exceeded. As soon as the axial force exceeds a certain value, the holding system of the belt strap at the belt latch becomes ineffective, and the belt strap is pulled in the longitudinal direction through the belt latch and the horizontal region of the belt strap is tensioned.
The connection of the belt strap with the belt latch, which can be opened up after a certain axial force has been exceeded, can be implemented, for example, in such a manner that the belt strap is sewn to the belt latch. However, it is also possible that the belt strap can be connected with the belt latch by a clamping fastener with a defined holding force.
In a further preferred embodiment of the invention, it is provided that the clamping fastener and the upper retractor, with which the diagonal region of the belt strap is connected, are electrically controllable such that (i) the upper retractor as well as the clamping fastener are released, (ii) after the withdrawal of a defined length of the belt strap, the upper retractor is locked, (iii) after the insertion of the belt latch into the belt buckle, the clamping fastener is locked and the upper retractor will be released, and (iv) in the event of an impact of the vehicle, the clamping mechanism will be released. In this embodiment, it is ensured that the air bag or inflatable region of the seat belt will always be in the upper position in which the occupant""s head is optimally protected. In addition, it is ensured that, for maintaining the maximal head protection function, the diagonal region of the belt strap can only be withdrawn from the upper retractor when, after locking the seat belt and the clamping fastener, the occupant moves his upper body toward the front. As soon as the occupant has returned into his rest position, the upper retractor will pull the slack from the diagonal region of the belt strap. The comfort of the three-point seat belt system will therefore be retained.
In a further preferred embodiment of the invention, the belt latch is constantly tightly connected with the belt strap and that a belt tightening device is assigned to the lower retractor.
When the seat belt is released from the occupant, the horizontal region of the belt strap is wound onto the lower retractor so that the belt latch comes to be situated on the seat surface and the region of the belt strap provided with the air bag rests vertically next to the seat on the interior side of the vehicle.
In order to protect an occupant who is not wearing the seat belt in the event of a side impact of the vehicle, it is provided that the gas generator connected with the air bag will be activated when the belt latch is not inserted into the belt buckle. The air bag is inflated by the gas generator so that the occupant not wearing the seat belt will be protected in the head region.
Three-point belt systems cannot be used with small children because of their small body size. As a result, safety functions are achieved by a specifically constructed child seat which is fixed by means of the seat belt with respect to the seat. So that the seat belt according to the invention can also be used in conjunction with such a child seat, according to a further preferred embodiment of the invention, a child seat detection system is provided which, when a child seat is detected, locks the upper retractor and prevents a triggering of the gas generator.